netdev - Re: [GIT PULL] virtio: fixes, features

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Message-Id: <38893b2e-c7a1-4ad2-b691-7fbcbbeb310f@app.fastmail.com>
Date:   Wed, 12 Oct 2022 23:06:54 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     xiujianfeng@...wei.com, kvm@...r.kernel.org,
        alvaro.karsz@...id-run.com, "Jason Wang" <jasowang@...hat.com>,
        angus.chen@...uarmicro.com, wangdeming@...pur.com,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Netdev <netdev@...r.kernel.org>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>, lingshan.zhu@...el.com,
        linuxppc-dev@...ts.ozlabs.org, gavinl@...dia.com
Subject: Re: [GIT PULL] virtio: fixes, features

On Wed, Oct 12, 2022, at 7:22 PM, Linus Torvalds wrote:
>
> The NO_IRQ thing is mainly actually defined by a few drivers that just
> never got converted to the proper world order, and even then you can
> see the confusion (ie some drivers use "-1", others use "0", and yet
> others use "((unsigned int)(-1)".

The last time I looked at removing it for arch/arm/, one problem was
that there were a number of platforms using IRQ 0 as a valid number.
We have converted most of them in the meantime, leaving now only
mach-rpc and mach-footbridge. For the other platforms, we just
renumbered all interrupts to add one, but footbridge apparently
relies on hardcoded ISA interrupts in device drivers. For rpc,
it looks like IRQ 0 (printer) already wouldn't work, and it
looks like there was never a driver referencing it either.

I see that openrisc and parisc also still define NO_IRQ to -1, but at
least openrisc already relies on 0 being the invalid IRQ (from
CONFIG_IRQ_DOMAIN), probably parisc as well.

     Arnd